Centrifuge with shaping of feed chamber to reduce wear

ABSTRACT

A centrifuge of the type having an outer bowl and an inner rotor both of which are generally cylindrical and rotate in the same direction but at slightly different rates separates slurry fed into the interior of the rotor into solids and liquid. An auger flight on the outside surface of the rotor carries the solids along the annular channel between the outside of the rotor and the inside of the bowl. The slurry is fed into a chamber at one end of the rotor and through outlet holes in the sides of the rotor into the channel. An end plate of the chamber has a forwardly projecting domed central nose which extends into the flowing slurry. Transverse guide plates of the rotor act to engage the slurry and accelerate it into rotation with the rotor before escaping through the holes. The guide plates are shaped with curved angularly projecting ribs on the downstream side in front of the hole over which the slurry flows in a smooth path before exiting the hole.

This invention relates to a centrifuge.

BACKGROUND OF THE INVENTION

Centrifuges have many different types and the present invention isconcerned with the two phase centrifuge type which provides high speedhorizontal decanting that separate solids from liquids. Centrifuges ofthis type have been manufactured by United Oilfield Inc., who areassignees of the present application for a number of years and eachincludes three primary parts which are the base or skid, the stainlesssteel case mounted on the skid and the rotating assembly consisting ofthe bowl, auger and gearbox which assembly is mounted in the stationarysteel case on the skid. The auger is mounted in the bowl so that thebowl surrounds the auger and both are mounted for coaxial rotation abouta longitudinal axis. The auger comprises generally a cylindrical bodycoaxial to the cylindrical bowl with an auger flight on its outersurface which has an edge close to the inside surface of the cylindricalbowl.

To create the desired effect, the bowl with the auger inside rotatesabout the axis at slightly different speeds in the same direction. Thebowl speed is variable depending upon the application and operatingconditions.

During operation, feed slurry is fed from an axially extendingstationary feed pipe at one end of the auger into a feed chamber at thatend of the auger through an end wall of the bowl. The flowing slurrystrikes an accelerator plate in the auger at one end of the feed chamberand is forced from the feed chamber outwardly into the bowl.

Centrifugal force causes heavier solids to accumulate on the insidesurface of the bowl. The auger, which is rotating with the bowl but at aslow speed relative to the bowl, acts to continuously drag them axiallyalong the bowl. Each of the bowl and the auger includes a tapered endportion at the feed end which converges radially inwardly toward adischarge end of the bowl, which is at the same end as the feed end. Therotation of the bowl and its tapered end tends to move the heaviermaterial axially away from the discharge end to the cylindrical sectionof greater diameter. Thus the auger drags the material along the taperedsection toward the discharge end. The discharge end includes dischargeports surrounding the feed duct so that the heavier solid material whenit reaches the discharge end is discharged outwardly by the centrifugalforce into the case for collection.

Finer solids are retained in the liquid traveling through the bowl awayfrom the feed end to the remote end but are deposited on the wall of thebowl and are continuously removed as they build-up inside the bowl bythe action of the auger and out the solids discharge ports.

Clean fluids travel towards the remote fluid end of the bowl and exitthrough adjustable eccentric ports at the remote fluid discharge end ofthe bowl. The centrifuge is commonly but not exclusively used for mudsystems in drilling where the mud is re-circulated through the drillstring to extract drilling solids so that the solids can be extracted inthe centrifuge and the clean fluid from the centrifuge can be recycledback into the mud system of the operation.

The greatest difficulty in achieving optimal performance in a centrifugeof this type is wear caused by the combined corrosive nature of flowpressure and the abrasive solids on the steel structure of thecentrifuge.

SUMMARY OF THE INVENTION

It is one object of the invention to provide an improved centrifuge ofthis general type.

According to one aspect of the invention there is provided a centrifugefor separation of particulates from a slurry containing the particulatesin a liquid comprising:

an outer bowl having a longitudinal axis and a peripheral wallsurrounding the axis, the peripheral wall extending from a first end ofthe bowl to a second opposed end of the bowl;

a first discharge arrangement at the first end of the bowl for dischargeof the particulates;

a second discharge arrangement at the second end of the bowl fordischarge of the slurry with the particulates removed;

a support assembly mounting the outer bowl for rotation about thelongitudinal axis such that the particulates in the slurry within thebowl tend to move radially outwardly of the axis toward an inner surfaceof the peripheral wall;

an inner rotor mounted coaxially within the outer bowl for rotation ofan outer wall of the inner rotor about the longitudinal axis, the rotorextending along the bowl from a first end of the rotor adjacent thefirst end of the bowl to a second end of the rotor adjacent the secondend of the bowl;

a drive system for driving rotation of the outer bowl and the innerrotor for common rotation in the same direction;

the drive system providing a differential in rotational speed betweenthe outer wall of the inner rotor and the inner surface of theperipheral wall of the outer bowl such that the outer wall movesangularly relative to the inner surface of the peripheral wall;

the outer wall of the rotor being spaced radially inwardly of the innersurface of the bowl so as to define a space therebetween within whichthe slurry is separated;

a helical auger flight carried on the outer wall of the rotor having anouter edge of the auger flight which moves relative to the inner surfaceof the peripheral wall so as to tend to carry particulates collecting onthe inner surface of the peripheral wall in a direction toward the firstend of the bowl and the first discharge arrangement located at the firstend;

the helical auger flight having openings therein allowing movement ofthe slurry in the space through the openings toward the second end ofthe bowl;

the bowl and the inner rotor each including a tapered portion such thatthe outer wall of the rotor and the inner surface of the bowl reduce indiameter toward the first end;

the rotor having a slurry inlet opening at the first end of the rotorinto a feed chamber within the rotor;

a slurry inlet duct for transporting the slurry through the first end ofthe bowl into the inlet opening in the first end of the rotor;

the rotor having at least one outlet opening in the outer wall to allowthe slurry to exit through the outer wall from the feed chamber into thespace;

the rotor having an end accelerator plate of the feed chamber mounted onthe rotor for rotation therewith;

the end accelerator plate lying generally in a radial plane of the axissuch that the slurry flowing generally axially into the feed chambercontacts the accelerator plate of the rotor and moves radially outwardlytherefrom through the at least one outlet opening into the space;

wherein the end accelerator plate includes a raised projecting memberthereon extending radially therefrom toward the slurry inlet opening.

Preferably the raised projecting member is dome shaped.

Preferably the raised projecting member is symmetrical about the axisand converges to an apex on the axis.

Preferably the raised projecting member extends to an outer edge thereofspaced inwardly of an edge of the end accelerator plate.

Preferably the at least one outlet opening is located in the taperedportion.

Preferably the rotor wall has a plurality of angularly spaced outletopenings each communicating with the feed chamber.

Preferably the rotor wall has a plurality of angularly spaced outletopenings each communicating with the feed chamber;

each outlet opening thus having a leading edge and a trailing edge whenconsidered relative to the direction of rotation of the rotor;

there is provided within the feed chamber a plurality of dischargesurfaces, each discharge surface extending between the trailing edge ofa respective one of the outlet openings and a leading edge of the nextoutlet opening so as to bridge a space therebetween;

each discharge surface being shaped, relative to an imaginary planejoining the trailing edge of a respective one of the outlet openings anda leading edge of the next outlet opening, such that a portion of thedischarge surface adjacent the leading edge of said next outlet definesa series of imaginary lines extending along the portion generallyparallel to the axis and lying in the discharge surface, which imaginarylines are angularly retarded relative to corresponding imaginary lineslying in the imaginary plane, where each line and its corresponding linein the plane are equidistantly spaced from the axis.

Preferably the portion of the discharge surface is smoothly curved incross-section taken in a radial plane of the axis.

Preferably the portion of the discharge surface has an apex which is ata maximum spacing from the imaginary plane where the apex is spaced fromthe leading edge and the surface tapers back toward the imaginary planeas it approaches the leading edge.

Preferably the portion of the discharge surface where the surface isretarded has a width in the direction between the leading edge and thetrailing edge which extends about half way across the imaginary plane.

Preferably each discharge surface is shaped, relative to the imaginaryplane, such that a portion of the discharge surface adjacent thetrailing edge of said one of the outlets lies generally in the imaginaryplane.

According to a second aspect of the invention there is provided acentrifuge for separation of particulates from a slurry containing theparticulates in a liquid comprising:

an outer bowl having a longitudinal axis and a peripheral wallsurrounding the axis, the peripheral wall extending from a first end ofthe bowl to a second opposed end of the bowl;

a first discharge arrangement at the first end of the bowl for dischargeof the particulates;

a second discharge arrangement at the second end of the bowl fordischarge of the slurry with the particulates removed;

a support assembly mounting the outer bowl for rotation about thelongitudinal axis such that the particulates in the slurry within thebowl tend to move radially outwardly of the axis toward an inner surfaceof the peripheral wall;

an inner rotor mounted coaxially within the outer bowl for rotation ofan outer wall of the inner rotor about the longitudinal axis, the rotorextending along the bowl from a first end of the rotor adjacent thefirst end of the bowl to a second end of the rotor adjacent the secondend of the bowl;

a drive system for driving rotation of the outer bowl and the innerrotor for common rotation in the same direction;

the drive system providing a differential in rotational speed betweenthe outer wall of the inner rotor and the inner surface of theperipheral wall of the outer bowl such that the outer wall movesangularly relative to the inner surface of the peripheral wall;

the outer wall of the rotor being spaced radially inwardly of the innersurface of the bowl so as to define a space therebetween within whichthe slurry is separated;

a helical auger flight carried on the outer wall of the rotor having anouter edge of the auger flight which moves relative to the inner surfaceof the peripheral wall so as to tend to carry particulates collecting onthe inner surface of the peripheral wall in a direction toward the firstend of the bowl and the first discharge arrangement located at the firstend;

the helical auger flight having openings therein allowing movement ofthe slurry in the space through the openings toward the second end ofthe bowl;

the bowl and the inner rotor each including a tapered portion such thatthe outer wall of the rotor and the inner surface of the bowl reduce indiameter toward the first end;

the rotor having a slurry inlet opening at the first end of the rotorinto a feed chamber within the rotor;

a slurry inlet duct for transporting the slurry through the first end ofthe bowl into the inlet opening in the first end of the rotor;

the rotor having a plurality of angularly spaced outlet openings eachcommunicating with the feed chamber to allow the slurry to exit throughthe outer wall from the feed chamber into the space;

the rotor having an end accelerator plate of the feed chamber mounted onthe rotor for rotation therewith;

the end accelerator plate lying generally in a radial plane of the axissuch that the slurry flowing generally axially into the feed chambercontacts the accelerator plate of the rotor and moves radially outwardlytherefrom through the at least one outlet opening into the space;

each outlet opening having a leading edge and a trailing edge whenconsidered relative to the direction of rotation of the rotor;

wherein there is provided within the feed chamber a plurality ofdischarge surfaces, each discharge surface extending between thetrailing edge of a respective one of the outlet openings and a leadingedge of the next outlet opening so as to bridge a space therebetween;

each discharge surface being shaped, relative to an imaginary planejoining the trailing edge of a respective one of the outlet openings anda leading edge of the next outlet opening, such that a portion of thedischarge surface adjacent the leading edge of said next outlet definesa series of imaginary lines extending along the portion generallyparallel to the axis and lying in the discharge surface, which imaginarylines are angularly retarded relative to corresponding imaginary lineslying in the imaginary plane, where each line and its corresponding linein the plane are equidistantly spaced from the axis.

Preferably the portion of the discharge surface is smoothly curved incross-section taken in a radial plane of the axis.

Preferably the portion of the discharge surface has an apex which is ata maximum spacing from the imaginary plane where the apex is spaced fromthe leading edge and the surface tapers back toward the imaginary planeas it approaches the leading edge.

Preferably the portion of the discharge surface where the surface isretarded has a width in the direction between the leading edge and thetrailing edge which extends about half way across the imaginary plane.

Preferably each discharge surface is shaped, relative to the imaginaryplane, such that a portion of the discharge surface adjacent thetrailing edge of said one of the outlets lies generally in the imaginaryplane. This forms a sharp edge at the junction with the wall of therotor which can better engage the slurry within the rotor.

Thus the accelerator plate is dominated by a “striker nose” thatprotrudes into the feed chamber. This adaptation can operate toeliminate splash-back, positions the flow, increases optimal performanceof the auger, and minimizes wear by forcing the solids to wear ontoother solids and avoid wearing on steel.

In addition, the slurry passes over the base of the feed chamber whichhas been re-designed with a curved surface to facilitate easier movementof solids and to make the area more resistant to wear. This area hasbeen accentuated to easier facilitate flow. By building up the height ofthe discharge edge or trailing of the feed chamber and giving it aslope, a path of least resistance is achieved.

After passing through the feed chamber, the slurry strikes anaccelerator plate and is forced into the bowl. The accelerator plate hasbeen designed to more readily force the materials into the bowl forseparation.

BRIEF DESCRIPTION OF THE DRAWINGS

One embodiment of the invention will now be described in conjunctionwith the accompanying drawings in which:

FIG. 1 is a partly schematic exploded view of a centrifuge according tothe present invention.

FIG. 2 is a partly schematic longitudinal cross sectional view of thecentrifuge of FIG. 1.

FIG. 3 is a cross sectional view along the lines 3-3 of FIG. 2.

FIG. 4 is a cross sectional view along the lines 4-4 of FIG. 3.

In the drawings like characters of reference indicate correspondingparts in the different figures.

DETAILED DESCRIPTION

In FIG. 1 is shown schematically a centrifuge of the type with which thepresent invention is concerned. Centrifuges of this type have beenmanufactured for a number of years by the present assignee and detailsof the general construction of this centrifuge is well known to oneskilled in the art.

The centrifuge generally comprises a base skid 10 on which is mounted ona fixed housing 11. The housing can be opened to access the interior ofthe housing and the elements therein. At one end of the housing isprovided a motor and gear box arrangement schematically indicated at 12which provides drive to the components inside the housing 11. At theother end of the housing is provided a feed duct 13 for supply of slurryfrom a source 14 through a duct 15.

Within the fixed housing 11 is provided an outer bowl 16 having aperipheral wall 17 with an inside surface 18. The bowl is mounted forrotation about a longitudinal axis 19 so that the inside surface of theperipheral wall rotates around the axis providing a centrifugal forceagainst the inside surface. The bowl is elongate along the axis 19 so asto provide a first end 20 and a second end 21. The first end 20 isgenerally a feed end so that the slurry from the source 14 is fed inthrough the duct 13 which passes through an opening 22 in the end 20 forentry into the interior of the bowl. The second end 21 is a dischargeend for the slurry and includes holes 24 through which the slurry canpass after separation of liquid from heavier particles so that theparticles are generally collected within the bowl allowing the liquidcomponent to escape through the holes 24 for collection within thehousing 11.

Inside the outer bowl 16 is provided a rotor 25 which is shaped tofollow generally the inside surface 18 of the bowl so that the rotoralso has a first end 26 adjacent the end 22 of that bowl and a secondend 27 adjacent the end 21 of the bowl. The rotor also has an outer wall28 which follows the general shape of the inside surface 18 but isspaced radially inwardly therefrom so as to define an annular space 30along the length of the rotor and along the length of the bowl. Thespace 30 defines a duct through which the slurry can pass while thecentrifugal action separates the particles onto the inside surface ofthe bowl while the liquid component tends to move along the bowl towardthe discharge end 21.

The motor and gear box 12 acts to drive the bowl through a firstcoupling 12A and acts to drive the rotor through a second coupling 12B.These are shown co-axial but this is merely schematic and suitable gearbox arrangements are well known to one skilled in the art to providethis driving arrangement.

In particular the motor and drive arrangement 12 acts to drive the bowland the rotor in a common rotation direction while providing arelatively small differential between the angular velocity of the bowland the angular velocity of the rotor. This relatively smalldifferential causes the outside surface of the wall 28 to moverelatively slowly in comparison with the common angular velocity,relative to the inside surface 18 of the peripheral wall of the bowl.

The wall 17 of the bowl has a cylindrical portion 17A extending from theend 21 to a position 17B, from which the wall 17 tapers radiallyinwardly toward the end 20. This forms a conical section 17C which istapered radially inwardly. It will be appreciated therefore that therotation of the bowl provides a force on materials on the portions 17Cof the wall of the bowl tending to cause those materials to move axiallytoward the end 21 and away from the end 20.

The wall 28 of the rotor also includes a cylindrical portion 28Aextending to a position 28B and includes a tapered portion 28C matchingthe taper 17C of the bowl.

On the outside surface of the wall 28 is provided an auger flight 32which is wrapped helically around the outer surface of the wall 28 fromthe end 21 through to the end 20 including along the tapered section28C. The flight is helically arranged at an angle such that thedifferential in angular rotation of the wall 28 relative to the bowlcauses the auger flight to sweep material collecting on the insidesurface 18 of the wall 16 along the wall 16 to the discharge end 20where it can be discharged from the bowl as collected solids. It will beappreciated that the heavy solids collect on the inside surface 18substantially immediately after the discharge into the space 30. Lightersolids flow along the space 30 through openings 33 in the flight 32toward the discharge end 24 but continue to accumulate on the insidesurface due to the centrifugal action on the particles. Such particleswhenever they collect on the inside surface are then carried by theoutside edge or ribbon of the flight along the wall to the end 20 of thebowl where they are discharged into the housing for collection in asuitable launder (not shown).

The duct 13 extends into the open end of the rotor at the end 26. Thusthe slurry enters into the hollow interior of the rotor and flows alongthe interior up to a closure plate 35 which bridges across the interiorof the rotor and halts the further forward flow of the slurry. Tworadially opposed holes 36A and 36B are provided in the outside wall ofthe rotor in the tapered section 28C for discharge of the slurryradially outwardly into the space 30.

Centrifuges of the above type are previously manufactured by the presentassignee and the centrifuge of this type is modified in the area of thefeed chamber 37 within the hollow interior between the end 26 and theacceleration plate 35. The feed chamber 37, the holes 36A and 36B andthe acceleration plate 35 are shown on an enlarged scale and in moredetail in FIGS. 3 and 4 which show the improvements of the presentinvention. Thus in FIG. 3 the wall 28C is shown which has two opposeddischarge holes 36A and 36B which are diametrically opposed relative toa center 19A on the axis 19. The hole 36A has a leading edge 38A and atrailing edge 38B relative to a direction of rotation R around the axis19. The opening 36B has a leading edge 39A and a trailing edge 39B againrelative to the direction of rotation. The holes 36A and 36B aregenerally rectangular so that the leading and trailing edges aregenerally parallel and extend along the tapered section 28C. While theholes 36A and 36B are shown rectangular, they may indeed be tapered inview of the taper in the wall 28C so that the leading and trailing edgesare not exactly parallel but converge together toward the end 26. Animaginary plane is indicated at P1 which interconnects the leading edge38A with the trailing edge 39B. Symmetrically a plane P2 which again isimaginary interconnects the leading edge 39A with the trailing edge 38B.These planes are defined merely for convenience of explanation of theshape and construction of a surface 40 which extends from the leadingedge 38A through to the trailing edge 39B. A symmetrical surface 41extends from the leading edge 39A to the trailing edge 38B. Thesesurfaces engage the material within the feed chamber 37. It will beappreciated that the surfaces 40 and 41 are rotating with the rotor atrelatively high velocity while the slurry entering through the duct 13is moving only in the axial direction. Thus the surfaces 40 and 41together with the acceleration plate 35 act to engage the fluid withinthe feed chamber 37 so as to accelerate the fluid in its rotation aroundthe axis 19 thus causing the fluid to move outwardly through thedischarge holes 36A and 36B.

The plate 35 is generally flat and circular in plan so as to fill theinterior of the rotor and define the end face of the feed chamber. Theacceleration plate 35 is modified by the addition of a nose 42 whichextends forwardly from the plate to an apex 43 spaced forwardly of theplate toward the end 26. The nose 42 is mounted on the axis 19 so as tobe symmetrical about the axis. The nose has a circular edge 44 at theplate surrounding the axis 19. The nose is dome shaped so that itconverges smoothly to the apex 43 with curved walls. The nose forms awear member which projects into the flow of the fluid from the mouth 13Aof the duct 13 so that the fluid tends to engage the nose at the apexand to spread around the surface 45 of the nose onto the plate 35 andits front surface 35A facing the fluid. The plate 35 is located at adownstream end 46 of each of the holes 36 with the holes extending withthe parallel upper and lower edges to an upstream end 47 just beyond themouth of the duct 13. Thus the material flowing onto the acceleratorplate 35 and its nose 42 is halted at that location thus causing thematerial to flow outwardly through the holes 36A and 36B. As thematerial begins to flow outwardly, it is engaged by the surfaces 40 and41 as best shown in FIG. 3. The surfaces are symmetrical so that onlyone of the surfaces will be described. Thus the surface 40 includes anend 40A commencing at the trailing edge 39B and from that end 40A it isflat extending to approximately a mid-point 40C. From that mid point itis curved rearwardly toward a rearward most point 40B. From that point40B, the surface 40 curves forwardly to a point 40D after which itreaches the plane P1. Thus it will be noted that each of a series oflines 40D, 40E, 40F are angularly retarded relative to points P3, P4, P5lying in the plane P2. It will be appreciated that all of these pointsor lines are purely imaginary and are used merely for explanation of theshape of the surface. Thus the point P3 lies at a common radial distancefrom the center 19A with the point 40D with each of the further pointscorresponding in radial distance. It will be noted that in the whole ofthe area between the edge 40A and the point 40C, the lines in thesurface are angularly retarded relative to corresponding lines withinthe plane P1. From the point 40C to the end 40A, the surface 40 is flatindicated at 40G. This provides on the surface 40 a rib 40H which israised relative to the imaginary plane P1.

This shape is formed by providing a part cylindrical wall 50 with oneedge 51 at the edge 40K and a second edge 52 attached to the wall 28C ata position behind the section 41G. Between the surface 40G and the point52, the surface 41 is made up from a filler material indicated at 53.The filler material can be weld or other materials which are resistantto the highly abrasive action of the particles within the fluid in thechamber 37.

The shaping of the surface 40 such that it is domed in an retardeddirection at the trailing end 40K assists in sweeping the material outof the opening 36B so that it flows more smoothly over the surface andout of the opening. In addition the curvature of the surface and thesmooth flowing action of the materials over the surface reduces the wearon the surface 40. As set forth above, the surface 41 is exactlysymmetrical so that it cooperates with the surface 40 as just described.

Thus the portion 40G of the surface 40 is a leading portion and rotatesinto the stationary or only slowly rotating slurry and acts to engagethis slurry and accelerate the slurry. The slurry then moves over thesurface 40 toward its end 40K at the opening 36B. The first part of thesurface in advance of the mid point 40C is flat and thus the slurryslides imply across this surface portion. However the second part of thesurface 40 between the mid point 40C and the end 40K is domed as theslurry begins to accelerate and move rapidly across this portion of thesurface. This domed shape which is retarded relative to the plane P1surprisingly allows smoother flow of the slurry with less wear on thesurface caused by the highly abrasive slurry. At the end 40K the surfacecurves forwardly toward the plane P1 so that at the edge 38A of theopening 36B the slurry can simply slide off the surface 40 through theleading edge 38A of the opening 36B. It will be noted that the junctionof the end 40A of the surface 40 with the wall 28C at the trailing edge39B of the opening 36A provides a sharpened edge or nose 60 which canbite into the slurry and cause it to move away from this edge toward theend 40K of the surface 40.

Since various modifications can be made in my invention as herein abovedescribed, and many apparently widely different embodiments of same madewithin the spirit and scope of the claims without department from suchspirit and scope, it is intended that all matter contained in theaccompanying specification shall be interpreted as illustrative only andnot in a limiting sense.

1. A centrifuge for separation of particulates from a slurry containingthe particulates in a liquid comprising: an outer bowl having alongitudinal axis and a peripheral wall surrounding the axis, theperipheral wall extending from a first end of the bowl to a secondopposed end of the bowl; a first discharge arrangement at the first endof the bowl for discharge of the particulates; a second dischargearrangement at the second end of the bowl for discharge of the slurrywith the particulates removed; a support assembly mounting the outerbowl for rotation about the longitudinal axis such that the particulatesin the slurry within the bowl tend to move radially outwardly of theaxis toward an inner surface of the peripheral wall; an inner rotormounted coaxially within the outer bowl for rotation of an outer wall ofthe inner rotor about the longitudinal axis, the rotor extending alongthe bowl from a first end of the rotor adjacent the first end of thebowl to a second end of the rotor adjacent the second end of the bowl; adrive system for driving rotation of the outer bowl and the inner rotorfor common rotation in the same direction; the drive system providing adifferential in rotational speed between the outer wall of the innerrotor and the inner surface of the peripheral wall of the outer bowlsuch that the outer wall moves angularly relative to the inner surfaceof the peripheral wall; the outer wall of the rotor being spacedradially inwardly of the inner surface of the bowl so as to define aspace therebetween within which the slurry is separated; a helical augerflight carried on the outer wall of the rotor having an outer edge ofthe auger flight which moves relative to the inner surface of theperipheral wall so as to tend to carry particulates collecting on theinner surface of the peripheral wall in a direction toward the first endof the bowl and the first discharge arrangement located at the firstend; the helical auger flight having openings therein allowing movementof the slurry in the space through the openings toward the second end ofthe bowl; the bowl and the inner rotor each including a tapered portionsuch that the outer wall of the rotor and the inner surface of the bowlreduce in diameter toward the first end; the rotor having a slurry inletopening at the first end of the rotor into a feed chamber within therotor; a slurry inlet duct for transporting the slurry through the firstend of the bowl into the inlet opening in the first end of the rotor;the rotor having at least one outlet opening in the outer wall to allowthe slurry to exit through the outer wall from the feed chamber into thespace; the rotor having an end accelerator plate of the feed chambermounted on the rotor for rotation therewith; the end accelerator platelying generally in a radial plane of the axis such that the slurryflowing generally axially into the feed chamber contacts the acceleratorplate of the rotor and moves radially outwardly therefrom through the atleast one outlet opening into the space; wherein the end acceleratorplate includes a raised projecting member thereon extending radiallytherefrom toward the slurry inlet opening.
 2. The centrifuge accordingto claim 1 wherein the raised projecting member is dome shaped.
 3. Thecentrifuge according to claim 1 wherein the raised projecting member issymmetrical about the axis and converges to an apex on the axis.
 4. Thecentrifuge according to claim 1 wherein the raised projecting memberextends to an outer edge thereof spaced inwardly of an edge of the endaccelerator plate.
 5. The centrifuge according to claim 1 wherein the atleast one outlet opening is located in the tapered portion.
 6. Thecentrifuge according to claim 1 wherein the rotor wall has a pluralityof angularly spaced outlet openings each communicating with the feedchamber.
 7. The centrifuge according to claim 1 wherein the rotor wallhas a plurality of angularly spaced outlet openings each communicatingwith the feed chamber; each outlet opening thus having a leading edgeand a trailing edge when considered relative to the direction ofrotation of the rotor; there is provided within the feed chamber aplurality of discharge surfaces, each discharge surface extendingbetween the trailing edge of a respective one of the outlet openings anda leading edge of the next outlet opening so as to bridge a spacetherebetween; each discharge surface being shaped, relative to animaginary plane joining the trailing edge of a respective one of theoutlet openings and a leading edge of the next outlet opening, such thata portion of the discharge surface adjacent the leading edge of saidnext outlet defines a series of imaginary lines extending along theportion generally parallel to the axis and lying in the dischargesurface, which imaginary lines are angularly retarded relative tocorresponding imaginary lines lying in the imaginary plane, where eachline and its corresponding line in the plane are equidistantly spacedfrom the axis.
 8. The centrifuge according to claim 7 wherein theportion of the discharge surface is smoothly curved in cross-sectiontaken in a radial plane of the axis.
 9. The centrifuge according toclaim 7 wherein the portion of the discharge surface has an apex whichis at a maximum spacing from the imaginary plane where the apex isspaced from the leading edge and the surface tapers back toward theimaginary plane as it approaches the leading edge.
 10. The centrifugeaccording to claim 7 wherein the portion of the discharge surface wherethe surface is retarded has a width in the direction between the leadingedge and the trailing edge which extends about half way across theimaginary plane.
 11. The centrifuge according to claim 7 wherein eachdischarge surface is shaped, relative to the imaginary plane, such thata portion of the discharge surface adjacent the trailing edge of saidone of the outlets lies generally in the imaginary plane.
 12. Acentrifuge for separation of particulates from a slurry containing theparticulates in a liquid comprising: an outer bowl having a longitudinalaxis and a peripheral wall surrounding the axis, the peripheral wallextending from a first end of the bowl to a second opposed end of thebowl; a first discharge arrangement at the first end of the bowl fordischarge of the particulates; a second discharge arrangement at thesecond end of the bowl for discharge of the slurry with the particulatesremoved; a support assembly mounting the outer bowl for rotation aboutthe longitudinal axis such that the particulates in the slurry withinthe bowl tend to move radially outwardly of the axis toward an innersurface of the peripheral wall; an inner rotor mounted coaxially withinthe outer bowl for rotation of an outer wall of the inner rotor aboutthe longitudinal axis, the rotor extending along the bowl from a firstend of the rotor adjacent the first end of the bowl to a second end ofthe rotor adjacent the second end of the bowl; a drive system fordriving rotation of the outer bowl and the inner rotor for commonrotation in the same direction; the drive system providing adifferential in rotational speed between the outer wall of the innerrotor and the inner surface of the peripheral wall of the outer bowlsuch that the outer wall moves angularly relative to the inner surfaceof the peripheral wall; the outer wall of the rotor being spacedradially inwardly of the inner surface of the bowl so as to define aspace therebetween within which the slurry is separated; a helical augerflight carried on the outer wall of the rotor having an outer edge ofthe auger flight which moves relative to the inner surface of theperipheral wall so as to tend to carry particulates collecting on theinner surface of the peripheral wall in a direction toward the first endof the bowl and the first discharge arrangement located at the firstend; the helical auger flight having openings therein allowing movementof the slurry in the space through the openings toward the second end ofthe bowl; the bowl and the inner rotor each including a tapered portionsuch that the outer wall of the rotor and the inner surface of the bowlreduce in diameter toward the first end; the rotor having a slurry inletopening at the first end of the rotor into a feed chamber within therotor; a slurry inlet duct for transporting the slurry through the firstend of the bowl into the inlet opening in the first end of the rotor;the rotor having a plurality of angularly spaced outlet openings eachcommunicating with the feed chamber to allow the slurry to exit throughthe outer wall from the feed chamber into the space; the rotor having anend accelerator plate of the feed chamber mounted on the rotor forrotation therewith; the end accelerator plate lying generally in aradial plane of the axis such that the slurry flowing generally axiallyinto the feed chamber contacts the accelerator plate of the rotor andmoves radially outwardly therefrom through the at least one outletopening into the space; each outlet opening having a leading edge and atrailing edge when considered relative to the direction of rotation ofthe rotor; wherein there is provided within the feed chamber a pluralityof discharge surfaces, each discharge surface extending between thetrailing edge of a respective one of the outlet openings and a leadingedge of the next outlet opening so as to bridge a space therebetween;each discharge surface being shaped, relative to an imaginary planejoining the trailing edge of a respective one of the outlet openings anda leading edge of the next outlet opening, such that a portion of thedischarge surface adjacent the leading edge of said next outlet definesa series of imaginary lines extending along the portion generallyparallel to the axis and lying in the discharge surface, which imaginarylines are angularly retarded relative to corresponding imaginary lineslying in the imaginary plane, where each line and its corresponding linein the plane are equidistantly spaced from the axis.
 13. The centrifugeaccording to claim 12 wherein the portion of the discharge surface issmoothly curved in cross-section taken in a radial plane of the axis.14. The centrifuge according to claim 12 wherein the portion of thedischarge surface has an apex which is at a maximum spacing from theimaginary plane where the apex is spaced from the leading edge and thesurface tapers back toward the imaginary plane as it approaches theleading edge.
 15. The centrifuge according to claim 12 wherein theportion of the discharge surface where the surface is retarded has awidth in the direction between the leading edge and the trailing edgewhich extends about half way across the imaginary plane.
 16. Thecentrifuge according to claim 12 wherein each discharge surface isshaped, relative to the imaginary plane, such that a portion of thedischarge surface adjacent the trailing edge of said one of the outletslies generally in the imaginary plane.